1. Field of the Invention
The present invention relates to a connector for two-way optical communications, the connector being connected to an optical plug holding a transmitting optical fiber and a receiving optical fiber.
2. Description of the Related Art
This kind of connector generally includes a light-emitting device, a light-receiving device, and light guides (light guiding members) for optically connecting the light-emitting device and the light-receiving device to the transmitting optical fiber and the receiving optical fiber of the opposite optical plug. For example, Patent document 1 (Japanese Patent Application Laid-Open No. 2001-133665) describes a connector configure thus.
In the connector of Patent document 1, a pair of receiving tubes is formed in a connector housing. The optical fibers (ferrules are placed on the ends of the fibers) of an optical plug are inserted in the receiving tubes. Light guides (referred to as sleeves in Patent document 1) are press-fitted into the receiving tubes and fixed at the back sides of the receiving tubes. However, in the fixation structure of such light guides, a stress caused by the press-fit may act on the light guides and the optical property (optical function) of the light guides may be deteriorated by the influence of the stress.
In order to avoid such a problem, the present applicant has already proposed, in Japanese Patent Application Laid-Open No. 2006-154788 (not publicly known on the priority date), light guides (light guide unit) and a connector using the same in which a pair of transmitting and receiving light guides is combined into a single unit via a connecting portion and the connecting portion is fixed by press fitting, so that a stress caused by the press-fit does not act on the light guides, that is, the optical property of the light guides is not deteriorated by the influence of the stress. Further, the coupling area of the connecting portion and the light guides is minimized to reduce a transmission loss caused by light leaking to the connecting portion integrally formed of the same material as the light guides and reduce cross talk occurring when transmitted light is incident on a light-receiving device of a local station, and components causing leakage of light are eliminated as much as possible.
FIGS. 1 to 5 show the configuration proposed in Japanese Patent Application Laid-Open No. 2006-154788. FIG. 1 shows the cross-sectional configuration of the connector. FIGS. 2 and 3 show the configuration of the light guide unit (referred to as an optical coupling member in Japanese Patent Application Laid-Open No. 2006-154788) and the configuration of a receptacle body, respectively. FIG. 4 shows the detail of the configuration of the attached light guide unit. FIG. 1 also shows optical fibers held by the ferrules of the opposite optical plug. In other words, FIG. 1 shows the optical fibers and ferrules in a state in which the optical plug is mated and connected. The illustration of optical fiber cores and a clad is omitted (the same in the following description).
The connector includes, as shown in FIG. 1, a receptacle body 10 made of resin, a light guide unit 20, a light-emitting device 30, a light-receiving device 40, a device holder 50, and a shield cover 60. In FIG. 1, reference numerals 71 and 72 denote a transmitting optical fiber and a receiving optical fiber of an optical plug, and reference numerals 73 and 74 denote ferrules respectively placed on the ends of the optical fibers.
In the light guide unit 20 of this example, as shown in FIG. 2, a pair of light guides 21 and 22 shaped like cylinders is combined into a single unit via a connecting portion 23. Further, the light guide unit 20 of this example is integrally formed by resin molding. Collimate lenses 21a and 21b and collimate lenses 22a and 22b are respectively formed on both end faces of the light guides 21 and 22. The illustration of the cores of the light guides 21 and 22 and a clad is omitted (the same in the following description).
The connecting portion 23 is configured as a plate and includes a base portion 24 and a pair of connecting ends 25 and 26 protruded from the base portion 24 in opposite directions along the plate surface. The connecting ends 25 and 26 are respectively connected to the sides (circumferential surfaces) of the axially intermediate portions of the light guides 21 and 22. Areas where the connecting ends 25 and 26 are connected to the circumferential surfaces of the light guides 21 and 22 are not larger than areas halfway around the light guides 21 and 22. Further, a large notch 27 shaped like a letter V is formed on the base portion 24.
As shown in FIG. 1, a recessed portion 11 is formed on the receptacle body 10. The opposite optical plug is inserted to the front of the recessed portion 11, and a pair of receiving tubes 12 is formed in the recessed portion 11. The pair of receiving tubes 12 is formed so as to protrude from a rear wall 13 of the receptacle body 10 making up the bottom surface of the recessed portion 11. The receiving tubes 12 include holes 12a, to which the ferrules 73 and 74 are inserted and fit, and through holes 14 continuing from the holes 12a. The through holes 14 connecting with the receiving tubes 12 are caused to penetrate the rear wall 13 and opened on a rear face (the outer side of the rear wall 13) 13a of the receptacle body 10.
As shown in FIG. 3, a recessed portion 15 corresponding to the outside shape of the connecting portion 23 of the light guide unit 20 is formed on the rear face 13a of the receptacle body 10. Further, guides 16 are formed outside the pair of through holes 14 so as to protrude halfway around the through holes 14. The inner circumferential surface of the guide 16 shaped like a semicylinder and the inner circumferential surface of the through hole 14 are flush with each other. As shown in FIG. 4, six protrusions 17 are formed on side wall surfaces formed along the depth direction in the recessed portion 15. The protrusions 17 are formed on positions at the same distances from the rear face 13a in the depth direction of the recessed portion 15, and the protrusions 17 are hemispherical in cross section.
The light guide unit 20 is attached to the receptacle body 10 by inserting the light guides 21 and 22 into the pair of through holes 14 from the rear face 13a of the receptacle body 10 and press-fitting the connecting portion 23 into the recessed portion 15. Thus, as shown in FIG. 4, the protrusions 17 are pressed and brought into contact with the connecting portion 23, so that the connecting portion 23 is positioned and fixed. At this point, the ends of the light guides 21 and 22 protrude on the side of the rear face 13a of the receptacle body 10, and a half of the circumference of each of the ends of the light guides 21 and 22 is held by the guide 16.
As shown in FIG. 1, the light-emitting device 30 and the light-receiving device 40 are stored and held in the device holder 50. In this example, the device holder 50 is stored and held in the shield cover 60. The shield cover 60 is attached to the receptacle body 10 from the rear face 13a, so that the light-emitting device 30 and the light-receiving device 40 are opposed to the end faces of the light guides 21 and 22, respectively. At this point, the pair of guides 16 formed so as to protrude on the rear face 13a of the receptacle body 10 is engaged and positioned in guide holes 31 and 41 formed on the light-emitting device 30 and the light-receiving device 40, respectively. Thus the optical axes of the light guides 21 and 22 and the optical axes of the light-emitting device 30 and the light-receiving device 40 are aligned with each other.
The transmitting optical fiber 71 and the receiving optical fiber 72 of the opposite optical plug are optically connected to the light-emitting device 30 and the light-receiving device 40 via the light guides 21 and 22, respectively. The transmitting optical fiber 71 and the receiving optical fiber 72 are held by the ferrules 73 and 74 and inserted into the receiving tubes 12.
In the connector configured thus, the light guide unit 20 is attached to the receptacle body 10 by press-fitting and fixing the connecting portion 23 into the recessed portion 15 of the receptacle body 10. Thus a stress caused by the press fitting does not act on the light guides 21 and 22, so that the optical property of the light guides 21 and 22 is not deteriorated by the stress.
Further, only the connecting ends 25 and 26 of the connecting portion 23 are connected to the light guides 21 and 22 and thus the coupling area of the connecting portion 23 and the light guides 21 and 22 is reduced. Thus leakage of light from the light guides 21 and 22 to the connecting portion 23 is suppressed. It is therefore possible to achieve a connector having high light transmission efficiency and less cross talk.
Incidentally, in the connector of FIGS. 1 to 5, the pair of guides 16 is formed so as to protrude on the rear face 13a of the receptacle body 10 and the guides 16 are engaged in guide holes 31 and 41 formed on the light-emitting device 30 and the light-receiving device 40, respectively. Thus the optical axes of the light guides 21 and 22 and the optical axes of the light-emitting device 30 and the light-receiving device 40 are aligned with each other (alignment). In this case, the connecting portion 23 is present between the light guides 21 and 22, and the light guides 21 and 22 are inserted into the through holes 14 from the rear face 13a of the receptacle body 10. For this reason, the guides 16 cannot be cylindrical. The guides 16 are, as described above, shaped like semicylinders to avoid the connecting portion 23.
Therefore, the guides 16 configured thus cannot hold the entire circumferences of the light guides 21 and 22. Thus, for example, in the event of molding strain on the receptacle body 10 and the light guide unit 20, misalignment may occur between the light guides 21 and 22 and the light-emitting device 30 and the light-receiving device 40.
FIG. 5A shows this state. FIG. 5A shows an example in which molding strain occurs on the receptacle body 10 and FIG. 5B shows an example in which molding strain occurs on the light guide unit 20. FIGS. 5A and 5B are both exaggerated for purposes of illustration. In FIGS. 5A and 5B, reference numerals 32 and 42 denote lenses formed on the light-emitting device 30 and the light-receiving device 40, respectively.
As shown in FIGS. 5A and 5B, when molding strain occurs on the receptacle body 10 or the light guide unit 20, the centers of the guides 16 formed into semicylinders in the receptacle body 10 and the centers of the light guides 21 and 22 are displaced from each other. On the other hand, the guides 16 are engaged in the guide holes 31 and 41 formed on the light-emitting device 30 and the light-receiving device 40, respectively. Thus the lenses 32 and 42 of the light-emitting device 30 and the light-receiving device 40 are respectively placed on the centers of the guides 16. Hence, when molding strain occurs on the receptacle body 10 or the light guide unit 20, the lenses 32 and 42 of the light-emitting device 30 and the light-receiving device 40 and the centers of the light guides 21 and 22 are displaced from each other as shown in FIGS. 5A and 5B, resulting in misalignment between the light guides 21 and 22 and the light-emitting device 30 and the light-receiving device 40.
Such misalignment causes a large loss of optical coupling between the light guides 21 and 22 and the light-emitting device 30 and the light-receiving device 40 and seriously deteriorates the optical property of the connector.